fix: remove unused async local storage middleware (#1817)

This middleware was made obsolete by e98b8d1.

Author: andrew0

__tests__/application/index.js

@@ -91,9 +91,4 @@ describe('app', () => {
     assert.deepStrictEqual(Koa.HttpError, CreateError.HttpError)
     assert.throws(() => { throw new CreateError(500, 'test error') }, Koa.HttpError)
   })
-
-  it('should export createAsyncCtxStorageMiddleware function', () => {
-    const app = new Koa()
-    assert.strictEqual(typeof app.createAsyncCtxStorageMiddleware, 'function')
-  })
 })

lib/application.js

@@ -248,15 +248,6 @@ module.exports = class Application extends Emitter {
   static get default () {
     return Application
   }
-
-  createAsyncCtxStorageMiddleware () {
-    const app = this
-    return async function asyncCtxStorage (ctx, next) {
-      await app.ctxStorage.run(ctx, async () => {
-        return await next()
-      })
-    }
-  }
 }
 
 /**